Screw rotor machines employable, both for compression or expansion of an elastic working fluid, have used asymmetric rotor profiles for improved efficiency of the compression or expansion process. The development of asymmetric screw rotor profiles is exemplified by U.S. Pat. Nos. 3,423,017, 4,140,445 and 4,435,139, assigned to Svenska Rotor Machiner: U.S. Pat. Nos. 4,053,263, 4,109,362 and 4,445,831 issued to the present applicant and assigned to Joy Manufacturing Company: U.S. Pat. No. 4,527,967 issued to the present applicant and assigned to Dunham-Bush, Incorporated; and U.S. Pat. Nos. 4,401,420 and 4,406,602 assigned to Hitachi Corporation.
Screw rotor machines, whether functioning as compressors or expanders, are normally of a cast or machined casing or housing bearing two parallel, laterally intersecting cylindrical bores opening at respective ends to high and low pressure ports. Within the bores there are mounted for rotation, interengaging helical screw rotors of the male and female type provided with helical lobes or land and intervening grooves having wrap angles normally less than 300 degrees. Typically, the male rotor is a rotor in which each lobe and groove has at least its major portion located outside the pitch circle of the rotor and has two generally convex flanks located outside the pitch circle, while the female rotor comprises a rotor in which each lobe and groove has at least its major portion located inside the pitch circle of the rotor and has two generally concave flanks located inside the pitch circle of the rotor.
With regard to existing patents covering assymetric screw rotor machines, the blow holes or leakage paths between compression or expansion chambers are relatively small on the discharge side which is controlled by the trailing male and female lobe and groove profiles.
Blowholes on the intake side which are controlled by leading male and female lobe and groove profiles are relatively large.
Driving and driven surfaces on all male drive rotor combinations are located on leading sides of male rotor lobes and female rotor grooves and these surfaces are designed for effective lobe action, without regard for the size of blowholes.
Screw rotor machines functioning as air compressors have previously been used to supercharge internal combustion engines. The relatively large blowholes present on the leading sides of male lobes and female grooves have, however, resulted in excessive leakage, which prevented the recovery of energy which was available due to the expansion of air in the machine.
It is therefore a primary objective of this invention to provide an improved screw rotor machine having improved screw rotor profiles resulting in minimized blowholes on both intake and discharge sides of the machine, effective lobe and groove driving surfaces and improved cutting conditions.
It is comtemplated that this will result in an internal combustion engine supercharger having the ability to act as a compressor when supercharging is required and an expander capable of recovering energy, when intake air, at atmospheric pressure, is expanded to the partial vacuum frequently present in internal combustion engine intake manifolds.